Month: January 2015

Categories
RCA Technical

The 1959 Ikegami-Tushin Limiter Inspired by the RCA BA6A

NHK_D_1Reader S. Komiya recently contacted us with some information regarding the Ikegami-Tushin limiting amplifier, an RCA BA-6A inspired piece that was built for Japanese broadcaster NHK in 1959.

SK has been so kind as to provide the schematic for this obscure device, as well as some background information.  I am posting the schematic full-size, so you can control-click it and download it for detailed viewing.

00_schematics_ikegami-limiter1959NHK_E1The photos in this post come from this Japanese auction website; the device pictured here recently sold for just Y30,000 ($300 USD).  And in working condition. 

600x450-2015011900002Here’s what SK has to say about the Ikegami-Tushin Limiter:

‘(It is) very much inspired by the RCA BA6A for sure.  It even looks a bit like it.  The tube format is very similar:  just change 6sk7 to 6ba6, 6j7 to 6au6 those goes into 6v6 PP and transformers between 6au6.  6ba6 were popular and cheap in japan because we made those a lot in japan in the 1950s and 60s.

6sk7 and 6j7 were never made in japan.  This unit also has an extra gain stage before first stage, which is pretty neat.  The components seem very high-end and some are custom made for this.  When i was gathering info about the ba6a in old tube shop, an older ham radio guy told me that he DIY’d one of these a long time ago…’NHKH_1NHKF_1*************

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20141230_123551SK also recently built his own BA6A from scratch.  It is depicted above, and you can hear audio samples of it at his soundcloud page.  SK has also scratch-built the Federal AM864 tube limiter, and he has this to say about the projects:

“The sound you will hear in soundcloud is a good comparison with the fed864.   The fed has good high open but compressed sound,  the ba6a has low mid, ton of low mid. I love them both.  The first time I used them was at a studio in Chicago back in 90s when I was living in US.  At that time I was using LA-2A mainly, but that studio had a Fed864 and BA6A.  They blew my mind, and since then I wanted them so bad!’

SK also provided some build-notes on his BA6A project; if you are planning on building you own BA6A, you might find these useful:  S_Komiya_RCA_Ba6a_DIY_notes

Categories
Technical Uncategorized

An DIY Tube Mixer Project c.1954

TubeMixer_DIY_1954Today’s article scan, again via reader Bill W., was written by one John S. Carroll and originally appeared in RADIO & TELEVISION news in 1954.  It describes a four-into-one mixer based on a design spec’d by UTC.

DOWNLOAD THE COMPLETE ARTICLE: 1954 Audio Mixer

1954_tube_mixer_rear1954_tube_mixer_bttmThere’s nothing terribly interesting about this particular circuit other than the output stage, which is push-pull and and is driven by a 3:1 interstage transformer which functions as both a phase inverter and provides a bit of additional voltage gain.

Output_stageI’ve never made a mic pre with a transformer phase inverter, but it could be very cool.  At Gold Coast Recorders one of the engineers’ favorite mic pre’s is a custom unit that I built based around an RCA 9362 cinema line amp (see earlier article here).  The 9362 is a push-pull output module, and it’s definitely a different sound – almost every tube mic pre made is single-ended.  Anyhow, at some point I will def build the circuit above into a mic pre.  Probably as soon as I find a pair of appropriate hi-fidelity (and shielded!) transformers for a buck.

1954_mixer_schematic

Categories
Technical

A DIY Broadcast Limiter Project circa 1955

1955_DIY_Limiter Courtesy of reader Bill W comes today’s scan of a much more complex tube limiter project.  Herbert Hartmann penned this 1955 article for RADIO & TELEVISION NEWS.

DOWNLOAD THE COMPLETE ARTICLE: 1955 Limiting Amplifier

Similar in principle to the Altec 436/438 and the Gates Sta-Level, the Hartmann unit is a Vari-Mu design.  As the author points out, the release time spec’d here is too fast to allow for totally distortion-free low frequency response.  If you’ve ever messed around with an Altec tube compressor, you will know that there is a real ‘limit’ to how fast you can make the release before distortion and artifacts emerge.  This was one of the real advantages of those insanely complex contemporary Fairchild and GE mastering and/or broadcast compressors, btw:  through some really inventive (and expensive) designs, they overcome the timing issues inherent in simpler devices like the Altecs and Gates units.  Here’s the Hartman schematic:

1955_limiter_SchemComments and suggestions are welcome,,,

Categories
Technical

A Simple One-Tube Compressor Circuit c.1953

1954_DIY_limiterReader Bill W recently sent us a few interesting ancient DIY audio projects that we had not seen before.  Today’s post is from RADIO-ELECTRONIC ENGINEERING and was written by one Ed C. Miller.

DOWNLOAD THE COMPLETE ARTICLE:Constant Output Broadcast Amplifier

The article details the operation and construction of the above-illustrated broadcast-remote mixer/amp, which includes a limiter.  While the overall unit is probably not something you’d want to ‘F’ with, the limiter component could be added to a DIY tube mic preamp (perhaps with a true-bypass switch).  One caveat: as the article warns, there are apparently ‘thumping’ artifacts inherent to this circuit, which was acceptable in its intended operation since it was designed for voice-frequency.

1954_limiter_SchemAnyhow, might be a fun project for a rainy day – build a pair of these into box with cheap 1:1 input transformers and simple line output stages?  Crush some room mics?  Anyone?

Categories
Early Digital Audio

The JVC 900 Digital Audio Mastering System of the early 1980s

JVC_1Download the complete sales materials for the circa 1982 JVC 900 series of digital-audio-mastering products:

DOWNLOAD: JVC_900_Digital_Audio_System

Products covered, with text, specs, and photos, include: the JVC AE-900V Digital Audio Editor, the DS-DM900 Digital Audio Mixer, the VP-900 Digital Audio Processor (AFAICT, a duplex stereo A/D, D/A), the TC-900V timecode unit, RM-900 remote, CR-850U 3/4″ ‘umatic’ tape machine, DS-FC901 Digital Interface Unit, DS-SU900 Sync unit, and BR-8600 1/2″ tape machine AKA a real expensive VCR.

JVC_digital_mastering_systemContributor Tom Fine told us, “this was a competitor to the Sony 1600 system.”  We’ve covered the early Sony units bit in the past (see here and here) – they were available early as 1978 – but I have never come across this JVC system before.  As Richard Hess writes in his very thorough blog,

“JVC had a competing (with SONY  -ed) and incompatible mastering system called the DAS-90 and later the DAS-900. …The processor in the DAS-90 system was called (at least at one point) the BP-90 while the processor in the DAS-900 series was the VP-900. The first version (DAS-90) used 3/4″ U-Matic video cassettes while the second version (DAS-900) used either U-Matic of VHS video cassettes (the latter to obtain longer playing time). I have not been able to confirm if tapes made on the DAS-90 can play on the DAS-900 or not. Early input says they are compatible and should interchange.”

JVC_900_mixerBut damn look at this lil 4×2 digital mixer!  It’s like a lil baby SSL!  And this is an actual digital mixer, btw – it’s just styled to look/feel like an analogue desk.  Crazy.

Anyone out there still using this system for anything?  Thoughts?  Let us know!